Thin and flexible multi-walled carbon nanotube/waterborne polyurethane composites with high-performance electromagnetic interference shielding

A type of lightweight and flexible multi-walled carbon nanotube (MWCNT)/waterborne polyurethane (WPU) composites is fabricated, which show superior shielding effectiveness (SE) of electromagnetic interference in the X-band even under the thin thickness of samples. The thickness values 0.05, 0.32 and 0.8 mm correspond to SE of 24, 49 and 80 dB, respectively. This attributes to the extremely high MWCNT loading up to 76 wt%. Moreover, the composites show much higher specific SE (up to 3408 dB cm²/g) than other carbon-based polymer composites with similar filler amount. Shielding mechanisms of the composites with wide ranges of MWCNT loadings are discussed based on the concentration, thickness and conductivity. High concentration of MWCNT/WPU composites at low thicknesses indicates higher capability of shielding by absorption compared to reflection, which is adverse to composites with relatively low MWCNT mass ratios. A comparison between experimental and theoretical SE results is made in detail based on observed microstructures by scanning electron microscopy. The MWCNT/WPU composite films fabricated on large-area polyimide and cloth substrates are also demonstrated.